Conventionally, a roller chain constructed as described-above is well-known, with the link plates being connected in a endless manner the roller chain is carried across a front chain gear and a rear chain gear, as shown in FIG. 7, so that a driving force is transmitted from the former gear to the latter gear.
As the roller chain circles around both the chain gears the outer link plates and inner link plates rotate relative to each other around the pins. To assist this rotation gaps are usually provided between the inner surfaces outer link plates and the outer surfaces inner link plates, and between the outer peripheries of the pins and the inner peripheries of the bushes to provide a smooth relative rotation of each outer link plate and inner link plate. Unfortunately, dirt or sand can enter the gaps between the pins and the bushes through the gaps between the outer and inner link plates. As a result, the frictional resistance between the pins and bushes increases producing noise and causing frequent wear and premature chain failure.
In order to overcome the above problem, a roller chain has been proposed which interposes elastic sealing members between the inner surfaces of outer link plates and the outer surfaces of the inner link plates, the elastic members always contacting with the opposite surfaces of both the link plates to prevent dirt or sand from entering the gaps between the pins and the bushes.
Such a roller chain, however, considerably increases the frictional resistance between the outer link plates and the inner link plates although the pins and bushes are free from added wear caused by dirt or sand, resulting in an unsmooth relative rotation between the inner and outer link plates.
Hence, the conventional chain, when carried across a front gear G.sub.1 and multi-stage rear gears G.sub.2 of a bicycle as shown in FIG. 7, cannot be switched smoothly among the rear gear through a derailleur for changing speed. Also, the chain, at its slack side, does not smoothly disengage from the front gear G.sub.1 and is raised in the rotating direction thereof to cause a wavelike motion, thus not only deteriorating the steerability of the bicycle but also producing noise.